The subject matter relates to an infusion unit that pressurizes and warm fluids for infusion into a body at pressures equal to or exceeding gravity. The subject matter also relates to a heat exchanger for an infusion unit in which fluids are warmed by the infusion unit. More particularly, the subject matter covers assisting extraction of the heat exchanger from the infusion unit by reducing friction between the heat exchanger and heating plates of the infusion unit.
Infusion relates to the introduction of a fluid into a body, usually, although not necessarily, into vasculature. A fluid that is infused into a body may be termed an “infusate”. Such fluids may include, for example, blood, blood products, and solutions such as saline, antibiotics, and medications.
The combination of low operating room temperatures and the administration of anesthetics which inhibit a patient's thermoregulatory function leads to hypothermia during surgery. As is known, perioperative hypothermia can produce adverse outcomes such as surgical wound infection, extended hospitalization, and blood loss. See Sessler D I: Complications and Treatment of Mild Hypothermia. ANESTHESEOLOGY 2001; 95:531-543. Prevention or mitigation of hypothermia, particularly perioperative hypothermia, is thus a key clinical factor for successful treatment outcomes.
Hypothermia may be accelerated by infusion of fluid, especially if the fluid is refrigerated. For example, Sessler indicates that a unit of refrigerated blood or a liter of crystalloid solution at room temperature decreases the mean body temperature of adults by approximately 0.25° C. Patients suffering from serious trauma may require rapid infusion of large amounts of fluid, which can cause a sharp and sudden loss of heat in the body core, leading to a drop in mean core body temperature. In order to prevent or mitigate infusion-caused heat loss in a trauma patient, the infusate is often heated as it is administered.
Warming fluid prior to infusion into a human or animal body is known. See, for example the intravenous fluid warming systems and appliances described in the cross-referenced patent documents. See also the Ranger® blood/fluid warming system and products described at www.arizant.com, the web site of Arizant Healthcare Inc. The Ranger® blood/fluid warming system includes a heating appliance and a disposable, relatively flat heat exchanger capable of being inserted into the heating appliance. Fluid flowing though the heat exchanger is warmed by contact between the heating appliance and heat exchanger, and then delivered intravenously to a patient.
An infusion system utilizes a heat exchanger including a flat, elongate fluid container that, under certain conditions, may be difficult to extract from between the fixed heating plates of a heating unit. When inserted in the heating unit, the heat exchanger is vertically oriented. During an infusion, the fluid container fills with pressurized infusate, which causes it to expand until its sides are pressed into close heat conducting contact with the heating plates. This close contact increases the friction between the sides of the fluid container and the heating plates. When infusion is halted or completed, friction caused by pressure exerted through the sides by infusate trapped in the fluid container may be great enough to prevent the heat exchanger from being easily extracted. In cases like these, and in other infusate warming cases where friction occurs between a flat fluid container and the fixed heating plates of a warming system heating unit, assistance may be needed in order to extract the heat exchanger from the heating unit